Piston



FIG. 1 is a perspective view of a piston showing my new design;

FIG. 2 is another perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof.

The broken lines shown in the drawing are for the purpose of illustrating environmental structure and form no part of the claimed design. 

CLAIM The ornamental design for a piston, as shown and described. 